Electric circuit



A g- 1950 E. L. PHILLIP] ET AL 2,517,131

ELECTRIC CIRCUIT Filed Dec. 16, 1949 'Ficgl.

a p FHA S E SHIFTER /3 24 j /7 e M l' 76 78 Inventors:

Earl Ll. Phillipi, C. Ronald Smith,

' Their Attorney.

Patented Aug. 1, 1950 ELECTRIC CIRCUIT Earl L. Phillipi, Schenectady, N. Y., and C. Ronald Smith, Seattle, Wash., assignors to General Electric Company, a corporation of New York Application December 16, 1949, Serial No. 133,284

2 Claims.

Our invention relates to electric circuits and more particularly to circuits of the type employed to provide relatively steep wave fronts of voltage in the firing circuits of electron discharge devices, such as thyratrons and the like. The principal object of the invention is to provide a new and improved circuit of the type mentioned which is a simple and inexpensive arrangement for obtaining an adjustable, narrow, and steep wave front peak of voltage in firing electron discharge devices and the like.

Our invention will be better understood from a consideration of the following description taken in connection with the figures of the accompanying drawing. In the drawing, Fig. 1 represents a phase-controlled rectifier system employing an electron discharge device and having a firing circuit embodying certain features of the invention; Fig. 2 shows certain characteristics of voltage and current in the arrangement of Fig. 1; and Fig. 3 represents a modification of the firing circuit shown in Fig. 1.

Referring now to Fig. 1, there is shown a rectifier comprising generally an electron discharge device I, which may be of the thyratron type, supplied with energy from an alternating current source 2, and arranged to supply a pulsating direct current to a load device 3. Thyratron I comprises a cathode 4, an anode 5, and a control electrode 6. Cathode 4 is connected to one terminal of source 2 and anode 5 is connected to one terminal of load device 3. The remaining terminal of load device 3 is connected to the other terminal of source 2.

Control electrode 6 is connected to a firing circuit, generally indicated by numeral I, which in turn is supplied with potential from source 2 through a phase shifting device 8 and a suitable isolating transformer 9. More particularly, the primary winding III of transformer 9 is connected to the terminals of source 2 and the secondary winding I I is connected to the input terminals of phase shifting device 8. The output terminals of phase shifting device 8 are con-' nected to input terminals I2 and I3 of firing circuit I.

Attention is next directed to the arrangement of firing circuit I which comprises an inductive element I4, a unidirectional conducting device I5, a capacitive element It, and a resistive element I'I. One terminal of inductance I4, which is preferably provided with an iron core, constitutes input terminal I2 of firing circuit I and accordingly is connected to one of the output terminals of phase shifter 8 as previously noted. The other terminal of inductance I4 is connected to cathode 4 of thyratron I, the connection between cathode 4 and inductance I4 forming an intermediate junction point I8 of firing circuit I.

Unidirectional conducting device I5 may conveniently be a dry-plate rectifier such as a selenium rectifier. One terminal of device I5 is connected to intermediate junction point I8 and the other terminal of device I5 constitutes input terminal I3 of firing circuit I. Unidirectional conducting device I5 is arranged to conduct current in firing circuit 1 from point I8 to point I3. Capacitance I6 is connected to terminal I3 and control electrode 6 of tl'iyratron I, the connection between capacitance I6 and electrode Ii forming an intermediate junction point I9 of firing circuit I. Resistance element I! is connected to points I8 and I9.

In the operation of the arrangement of Fig. 1, thyratron I is rendered conductive when the potential of anode 5 is made positive with respect to the potential of cathode 4 and when a suitable impulse voltage, also positive with respect to cathode 4, is simultaneously applied to control electrode 6 by action of firing circuit 1. Since potential is supplied to thyratron I from alternating current source 2, thyratron I is rendered alternately conductive and non-conductive and thus a unidirectional current of pulsating nature is supplied to load device 3. By the use of phaseshifting device 8 the magnitude of the current supplied to load 3 may be varied in accordance with well-known principles.

Attention is next directed to the operation of firing circuit I, the function whereof is to supplyresistance I1 and capacitance I6 is relatively small compared with the current fiowing through unidirectional conducting device I5. ducting path through resistance I I and capacitance It serves as a discharge path for capacitance I6, as will presently be more fully de-,

scribed.

When the potential of terminal I2 is positive.

with respect to the potential of terminal I3, cathode 4 is likewise positive with respect to control electrode 6. As is well-known however, the combination of a control electrode and a cathode in an electron discharge device such as thyratron I' constitutes a unidirectional conducting path under normal conditions of operation, and the normal flow of current through such a path is from the control electrode to the cathode or, in the present case, from control electrode 6 to cathode 4. Accordingly when cathode 4 is positive with respect to control electrode 6, no current fiows from control electrode 6 to cathode 4.

Since the potential impressed on input terminals I2 and I3 is alternating in nature, terminal The con-.

l2 becomes negative with respect to terminal 13 during half. of each cycle of the impressed potential, andunder this condition the flow of current in inductance l4 and unidirectional conducting device i5 tends to be arrested. Howevenfidue to the presence of inductance I l, the current flowing through unidirectional conductor is tends to be maintained and therefore the decay of the current to substantially zero is delayed and is made to occur during the half cycle'when such current normally does not flow because of reversal of polarity of the impressed voltage.

Since conduction does not occur in a reverse direction through device l5, when the forward current therethrough ceases to flow an inverse potential is suddenly impressed thereacross, and by proper choice of inductance M the sudden increase of potential across device may be made to'occur near the peak value of the alter nating potential. Thus a potential difference approximately equal to the peak value of the alternating potential exists between points l3 and I8, point 23 being positive with respectto point l8, and this potential difference is impressed on theseries combination of capacitor i5 and the unidirectional conducting path formed by control electrode 6 and cathode l. When electrode 6 is positive with respect to cathode i current may be conducted from the former to the latter, and accordingly, capacitor 56 is rapidly charged by the voltage impressed between points l3 and I8, and during the charging period an impulse of current flows from control electrode a to cathode 4.

Following the charging of capacitance iii the potential between points it and i8 decreases to zero, in accordance with the normal mode of the alternating potential impressed on firing circuit 1; Subsequently the alternating potential increases in a reverse direction, causing point 12 again to bepositive with respect to point l3, and causing a new charging cycle of capacitance [8 to be initiated. However, capacitance [6 possesses a charge from the previous charging sycle and unless a discharging arrangement is provided the desired action of again charging capacitance [6' cannot be effected. Accordingly resistance ing circuit 1 of Fig. 1 except that a second unidirectional conducting device 24, which may conveniently be similar to device I5, is shown connected from points l9 to It in place of the unidirectional conducting path formed by control electrode ii and cathode l in Fig. 1. Unidirectional conducting device 2 3 is arranged to conduct current in a direction from point [9 to point it, or in other words unidirectional conducting devices l5 and 24 are arranged to conduct current in opposite directions with respect to intermediate junction point It. The operation of the network shown in Fig. 3 is in general similar to the operation of firing circuit 1 shown in Fig. l, and the characteristics of the voltage impressed across unidirectional conducting device 24 and the current flowing therethrough are similar to characteristic curves 28 and 2!, respectively, shown in Fig. 2.

While we have shown and described certain preferred embodiments of our invention, it will be understood that our invention may well take other forms and we, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention. i

What we claim as new and desire to secure by 1 Letters Patent of the United States is:

I T is provided as a discharge path for capacitance [6. Discharge of capacitance it is effected during the half cycle of the impressed potential when input terminal [2 is positive with respect 1- to input terminal [3, thereby preparing capacitance It for recharging during the following half cycle:

Referring now to Fig. 2, there are shown characteristic curves 20 and 2|, respectively, of the voltage between control electrode 6 and cathode 4 and the corresponding current flowing from the former to the latter, as provided by action of firing circuit 1. It will be seen that a series of periodic voltage peaks 22, having relatively sharp rates of increase and decrease, and a sefies of corresponding current impulses 23 are provided to initiate firing of thyratron I during 1. In a firing circuit, an electron discharge device having a cathode, an anode and a control electrode, a unidirectional conducting device, means to impress alternately forward and inverse voltages on said device, said forward voltage causing periodic pulses of current to be conducted by said device, said current pulses tending to decay to zero upon reversal of said voltage from forward to inverse, inductive means to delay said decay and cause occurrence thereof during the period when said. inverse voltage is impressed on said device, a capacitance connected to form a series combination with said cathode and said control electrode, said combination being subjected to a voltage responsive to the voltage impressed on said unidirectional conducting device, charging of said capacitance being effected by said inverse voltage, and means including a resistance to discharge said capacitance during the period when said forward voltage is impressed on said device.

2. An electric network comprising an inductive element, one terminal of said element constituting a first input terminal of said network and the other terminal of said element forming a first intermediate junction point of said network, a first unidirectional conducting device, one terminal of said device being connected to said first intermediate junction point and the other terminal of said device constituting a second input terminal of said network, said first and second input terminals being connected to an alternating current source, a capacitive element, one terminal of said capacitive element being connected to said second input terminal and the other terminal of said capacitive element forming a second intermediate junction point of said network, a resistive element connected to said first and secondintermediate junction points, and a second unidirectional conducting device connected to said first and second intermediate junction points, said first and second unidirectional conducting devices being oppositely poled with respect to said first intermediate junction point i EARL L. PHILLIPI'.

C. RONALD SMITH.

No references cited. 

